Increasing the signal to noise ratio (SNR) of audio systems is generally motivating by a desire to increase the speech intelligibility in a noisy environment, for purposes of voice communications and machine-control via automatic speech recognition.
A common system to increase SNR is using directional enhancement systems, such as the “beam-forming” systems. Beamforming or “spatial filtering” is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in a phased array in such a way that signals at particular angles experience constructive interference while others experience destructive interference.
The improvement compared with omnidirectional reception is known as the receive gain. For beamforming applications with multiple microphones, the receive gain, measured as an improvement in SNR, is about 3 dB for every additional microphone, i.e. 3 dB improvement for 2 microphones, 6 dB for 3 microphones etc. This improvement occurs only at sound frequencies where the wavelength is above the spacing of the microphones.
The beamforming approaches are directed to arrays where the microphones are spaced wide with respect to one another. There is also a need for a method and device for directional enhancement of sound using small microphone arrays.